Geologic hazards Flashcards
Types of landslides
- Rotational landslide
- translational landslide
- block slide
- rockfall
- topple
- earthflow
- lateral spread
- debris flow
- debris avalanche
- creep
is the downslope movement of Earth material , primarily under the influence of gravity. The word landslide is a general term for this and for the landforms created by such movements.
Mass wasting
Mass wasting is classified into three sub-categories:
flow, slide, and fall.
Individual particles move downslope independently of one another , not as a consolidated mass. Typically occurs in loose, unconsolidated regolith
type of mass wasting
Flow
Material Moves as discrete blocks; can occur in regolith or bedrock
type of mass wasting
slide
material falls freely in air; typically occurs in bedrock
type of mass wasting
fall
subcategory of Flow (4)
Creep
debris flow
earthflow and mudflow
solifluction
subcategory of slide (2)
slump
rockslide
Slow, visually imperceptible movement
subcategory of flow
creep
More than half the particles larger than sand size; rate of movement varies from less than 1m/year to 100km/hr or more
subcategory of flow
debris flow
morement of fine-grained particles with large amounts of water
subcategory of flow
earthflow and mudflow
Morement of waterlogged soil generally over permafrost
subcategory of flow
solifluction
Downward slipping of a block of earth material, usually with a backward rotation on a concave surface
subcategory of slide
slump
Usually rapid movement of a newly detached segment of bedrock
subcategory of slide
rockslide
Factors that Control Mass Wasting (5)
- Steepness of the slope
- Type of rock and orientation of rock layers
- Nature of consolidated materials
- Water and vegetation
- Earthquakes and volcanoes
this is a factor in mass wasting. If frost wedging dislodges a rock from a steep cliff, the rock tumbles to the valley below. However, a similar rock is less likely to roll down a gentle hillside.
Steepness of the slope
Imagine a hill underlain by shale, sandstone, and limestone oriented so that their bedding lies parallel to the slope. If the base of the hill is undercut, the upper layers may slide over the weak shale. In contrast, if the rock layers dip at an angle to the hillside, the slope may be stable even if it is undercut. Therefore, a geologist or engineer must consider not only a slope’s stability before construction, but how the project might alter its stability.
Type of rock and orientation of rock layers
The angle of repose is the maximum slope or steepness at which loose material remains stable. If the slope becomes steeper than the angle of repose, the material slides.
Nature of consolidated materials
To understand how water affects slope stability, think of a sand castle. Even a novice sand-castle builder knows that the sand must be moistened to build steep walls and towers, but too much water causes the walls to collapse. Small amounts of water bind sand grains together because the electrical charges of water molecules attract the grains. However, excess water lubricates the sand and adds weight to a slope.
Water and vegetation
An ________ may cause mass wasting by shaking an unstable slope, causing it to slide. A ________ may melt snow and ice near the top of a volcano. The water then soaks into the slope to release a landslide.
Earthquakes and volcanoes
Predicting and Avoiding Landslides
Landslides commonly occur on the same slopes as earlier landslides because the geologic conditions that cause mass wasting tend to be constant over a large area and remain constant for long periods of time. Thus, if a hillside has slumped, nearby hills may also be vulnerable to mass wasting.
In addition, landslides and mudflows commonly follow the paths of previous slides and flows.
Awareness and avoidance are the most effective defenses against mass wasting. Geologists construct maps of slope and soil stability by combining data on soil and bedrock stability, slope angle, and history of slope failure in the area. They include evaluations of the probability of a triggering event, such as a volcanic eruption or earthquake. Building codes then regulate or prohibit construction in unstable areas.
is a sudden motion or trembling of the Earth caused by the abrupt release of energy that is stored in rocks.
A rock stores elastic energy when it is distorted by a tectonic force. When the rock fractures, it snaps back to its original shape, creating an __________.
Earthquakes
is the study of earthquakes and the nature of the Earth’s interior based on evidence from seismic waves.
Seismology
Types of Earthquake (2)
Tectonic earthquake
Volcanic Earthquake
the energy stored in the crust causes the tectonic plates to move towards, away, or push against each other. With time the stored energy and the movement of the tectonic plates build up the enormous pressure within the region between two plates
Tectonic earthquake
Earthquake-related to the volcanic activity are called a ____________. The magnitude of these quakes is usually weak
Volcanic earthquake
is a measure of earthquake size and remains unchanged with distance from the earthquake. This is expressed by the Richter Scale.
Magnitude
describes the degree of shaking caused by an earthquake at a given place and decreases with distance from the earthquake epicenter . This is expressed by the Mercalli Scale.
Intensity
is a logarithmic scale that calculates earthquake size by measuring ground motion on seismographs
Richter Scale
earthquakes may cause grains of water-saturated soil to shift closer together, subsequently losing their shear strength and will allow the grains to behave as a fluid.
Liquefaction
Earthquake prediction
Long-term earthquake prediction is based on the observation that most earthquakes occur at tectonic plate boundaries.
Short-term prediction is based on occurrences of foreshocks, release of radon gas, changes in the land surface, the water table, electrical conductivity, and erratic animal behavior.
Other Geologic Hazards (5)
Volcanic Eruption
Avalanche
Subsidence
Flood
Tsunami
iswhen gas and/or lava are released from a volcano —sometimes explosively.
Volcanic Eruption
is a rapid flow of snow down a slope, such as a hill or mountain. This can be set off spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, other animals, and earthquakes.
avalanche
is a general term for downward vertical movement of the Earth’s surface , which can be caused by both natural processes and human activities. This involves little or no horizontal movement, which distinguishes it from slope movement.
Subsidence
This occurs in known floodplains when prolonged rainfall over several days, intense rainfall over a short period of time, or a debris jam causes a river or stream to overflow and flood the surrounding area.
When rain falls, the surface runoff can move very quickly from mountainous or hilly areas to low lying areas making these low lying areas more prone to flooding
Flood
When an earthquake occurs beneath the sea, part of the sea floor rises or falls. Water is displaced in response to the rock movement, forming a wave. Sea waves produced by an earthquake are called by their Japanese name, ________.
Tsunami
